Method of sealing electric blasting caps



May 22, 1962 J, L BASH, JR" ET AL 3,035,474

METHOD OF SEALING ELECTRIC BLASTING CAPS Filed July 28, 1958 FlGi FIG. 2 FIG. 5

INVENTORS. JOHN LA BASH JR. By MELVIN 1-:v EILERS ATTOPMG any United States Patent Ofiice 3,035,474 METHQD OF SEALING ELECTRIC BLASTHNG CAPS John La Bash, Jr., Indianapolis, Ind., and Melvin E. Eilers, Gillespie, Ill., assignors to Olin Mathieson Chemical Corporation, East Alton, 11]., a corporation of Virginia Filed July 28, 1958, Ser. No. 752,158 6 Claims. (Cl. 861) This invention relates to electric blasting caps and particularly to electric blasting caps having improved closures and a method of making them.

Electric detonators usually consist of an explosive train contained in a cylindrical metal cup. This explosive train is initiated by a resistance or bridge wire embedded in a sensitive explosive within the case; the electric lead wires have a bridge plug molded about them and positioned immediately above the igniter mix. The detonator is then sealed by pouring a relatively deep layer of a waterproofing composition such as pitch in place while in a heated fluid condition, and subsequently rendered non-fluid by cooling to normal temperature. This pitch seal is normally held in place by pouring a layer of sulfur over it.

While detonators sealed in this manner have been found to be generally satisfactory, they exhibit definite shortcomings when exposed to atmospheric conditions met in a number of military and commercial applications. Thus, when this type of detonator is subjected to an exceedingly low temperature, say about 65 F., the pitch will contract from the inner wall of the case, thus destroying the seal. On the other hand, high temperatures i in the neighborhood of 100 F. to 125 F. and above cause the pitch or other waterproofing material to become fluid and difiicult to maintain in its proper position.

Thus, it is apparent that the value of such detonators is limited to a relatively narrow operational temperature range. Furthermore, detonators sealed in this manner are deficient in pull strength at elevated temperatures; that is, the bridge plug can be rather easily separated from the detonator case by pulling on the lead wires.

It is, therefore, an object of this invention to provide a novel, improved electric detonator closure and a method of making it. Another object of this invention is to provide an electric detonator seal that will maintain its effectiveness over Wide temperature ranges. Still another object of this invention is to provide a detonator seal that positively secures the bridge plug within the detonator case.

Other objects will become apparent to those skilled in the art when the following description is read in connection with the accompanying drawing in which:

FIGURE 1 is a view in side elevation, partially in section, of an electricblasting cap constructed in accordance with the present invention;

FIGURE 2 is a similar view of a detonator made in accordance with this invention but taken at an angle of 180 relative to FIGURE 1;

FIGURE 3 is a view in side elevation of the detonator of FIGURE 1 and is taken at an angle of 90 relative to FIGURE 1;

FIGURE 4 is a cross-sectional view taken along the line IV-IV of FIGURE 1; and

FIGURE 5 is a cross-sectional view corresponding to FIGURE 4 but showing another embodiment of the invention.

The novel closure of the present invention relies upon an elastomer polymerized in place above the bridge plug together with a crimp that reduces the cross-sectional area of the mouth of the detonator. More specifically, this invention contemplates a detonator with a metal case which is crimped about and between the spaced lead wires emerging from the bridge plug. That portion of merizable elastomer.

The elastomer is introducedinto the open end of the detonator case above the bridge plug in a liquid or plastic condition and is subsequently polymerized in place. The elastomer can be added prior to the crimping operation.

If this is done, it is preferred that the lead wires in the case above the bridge plug are thoroughly wet with the unpolymerized elastomer to insure an effective seal. Also, the volume of the elastomer injected into the open end of the detonator case is suflicient to fill the mouth of the case after it has been crimped. Alternately, the mouth of the detonator case can be crimped and the liquid polymer izable elastomer then injected into the open end of the detonator. In either event, the elastomer is cured or polymerized in place to completethe detonator seal.

The polymerizable elastomer utilized in accordance with. this .invention must be one .thatis liquid in its unpolymerized .state and is capable of being polymerized or cured to form a. rubber-like solid. Preferably, the

present invention contemplates the utilization of an elastomeric composition that is solvent-free. In those cases 'i in which a solvent is used, the solvent must be one that has no deleterious effects upon the explosive charge in the detonator. If this precaution is not taken, the explosive train may be desensitized by the'solvent present in the composition. The elastomeric compositions can generally be cured by permitting them to stand at room tem-' perature for a prolonged period. It is preferred, however,

to accelerate the curing process by heating the detonator at a temperature well below'the flash point of any of the components of the explosive train. In this Way, the elastomer can be fully set in a relatively short period.

The polysulfide' liquid polymers have been found particularly suitable in the preparation of the detonator seal of this invention. These polysulfide liquid polymers are commercially available and have molecular weights in the general neighborhood of 300, 1,000, and 4,000. They are commercially produced from polymers of initially much higher molecular weight made by reaction of di(chloroethyl) formal with sodium polysulfide in the presence of a small amount of 1,2,3-trichloropropane. This reaction yields low molecular weight branched polymers with terminal thiol groups. Curing of these polysulfides is normally accomplished by oxidation of the disulfide linkages. While liquid polysulfides of the above type are preferred, other types of liquid polymerizable elastomeric compositions, such as polychloroprene and the like can also be used.

The crimp of the present invention can be obtained by any conventional means. It is preferred, however, that the detonator be crimped by placing it between two cooperating dies of the proper configuration. This is most readily accomplished by securing the assembled detonator in a suitable fixture and permitting a pair of oppositely disposed dies to converge upon the detonator in the area proximate its open end.

With reference to the drawing, the detonator is provided with an aluminum case 1 containing an explosive train consisting of a consolidated base charge 2 of cyclonite, a pressed initiating charge 3 of lead azide and a relatively loose ignition charge 4 of lead styphnate. A molded sulfur bridge plug 5 carrying a pair of spaced lead wires 6 V Patented May 22,1962

The crimped,

is positioned above the ignition charge and the ends of the lead wires are joined together by bridge wire 7 which is embedded in the ignition charge. In this embodiment, the plastic insulation 8 for the lead Wires terminates a short distance from the sulfur plug. That portion of the detonator case above the bridge plug is completely filled with a polymerized liquid polysulfide elastomeric composition designated as 9.

The open end of the detonator is crimped about each of the lead wires as shown at 10. That portion of the mouth of the case between the lead wires is distorted to form an axial cavity intermediate the lead wires. This cavity is formed by the general concave face 11 as illustrated in FIGURES 1 and 4 and the oppositely disposed convex face 12 as shown in FIGURES 2, 3 and 4. The configuration of the resultant intermediate cavity is best illustrated in FIGURE 4.

The detonator of this embodiment was prepared by crimping the mouth of the case about and between the spaced lead wires as described above and a sufficient amount of a liquid polysulfide composition was injected into the intermediate cavity to completely fill that portion of the detonator case above the bridge plug. This polysulfide composition was solvent-free and had the following approximate composition, expressed in parts by weight:

Parts Liquid polysulfide 30 Phenol formaldehyde resin 30 Stearic acid 3 Zinc sulfide 7 Barium sulfate 30 This composition contained about 10% of an accelerator consisting essentially of:

The seal was completed when the polysulfide composition was cured by subjecting the completed detonator to a temperature of 50 C. for approximately 16 hours.

In those instances Where it is desired to position the elastomeric composition in place prior to crimping, it has been found preferable to provide the detonator with a crimp of the type shown in FIGURE in which that portion of the detonator case between the lead wires is substantially crimped together.

Detonators prepared in accordance with the above embodiment function effectively even after they have been stored for several hours at 65 F. followed by prolonged storage at 125 F. Neither were such detonators effected by prolonged water immersion under pressures of 100 p.s.i. at about 65 F. These detonators also showed remarkable pull strength and when the lead wires were subjected to pull test, they broke before the bridge plug could be pulled out of the detonator case.

The term electric blasting cap is used herein as a generic term to include all types of electric explosive initiators. Thus, the present invention is applicable with equal facility to electric detonators, electric blasting caps, electric squibs and similar devices.

From the foregoing description, those skilled in the art should readily understand that the invention accomplishes its objects and provides a substantially improved detonator seal and a method of making it. While one comlete embodiment of the invention has been disclosed in detail and modifications indicated, it is not to be understood that the invention is limited to the details of the disclosure, but that such modifications and variations thereof as do not depart from the spirit of the invention are contemplated by and within the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. A method of sealing an electric blasting cap having a metallic case open at one end and containing an explosive charge comprising, inserting a bridge plug carrying a pair of spaced lead wires into the case and above the explosive charge, crimping the open end of the case about and between the lead wires above the bridge plug, the crimping being restricted to that portion of the case above the bridge plug, substantially filling that portion of the case above the bridge plug with a liquid polymerizable elastomer, and polymerizing the elastomer, the elastomer polymerized in place constituting the sole means of sealing the blasting cap.

2. The method of claim 1 in which the open end of the blasting cap is crimped into 3 connected compartments, 2 of which contain the lead wires and the remaining compartment positioned between them.

3. The method of claim 1 in which the elastomer is a solvent-free, synthetic polysulfide rubber.

4. The method of claim 3 in which the elastomer is a solvent-free, synthetic polysulfide rubber.

5. A method of sealing an electric blasting cap having a metallic case open at one end and containing an explosive charge comprising, inserting a bridge plug carrying a pair of spaced lead wires into the case and above the explosive charge, partially filling that portion of the case above the bridge plug with a liquid, polymerizable elastomer, wetting the lead wires above the bridge plug therewith, crimping the open end of the case about and between the lead wires above the bridge plug, the crimping being restricted to that portion of the case above the bridge plug, and polymerizing the elastomer, the elastomer polymerized in place constituting the sole means of sealing the blasting cap.

6. A method of sealing an electric blasting cap having a metallic case open at one end and containing an explosive charge which comprises inserting a bridge plug carrying a pair of spaced lead wires into the case and above the explosive charge, deforming the open end of the case about and between the lead wires above the plug so that portions of the case are positioned about each lead wire in the form of a partial circle with an arcuate space between the lead wires and the adjacent portions of the case, the remainder of the deformed portion of the case being positioned between the lead wires, the crimping being restricted to that portion of the case above the bridge plug, filling that portion of the case above the plug with a liquid polymerizable elastomer, and subsequently polymerizing the elastomer, the elastomer polymerized in place constituting the sole means of sealing the blasting cap.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,835 Noddin Aug. 10, 1954 2,695,563 Mulqueeny Nov. 30, 1954 2,722,155 Pauls Nov. 1, 1955 2,750,831 Long June 19, 1956 2,756,645 Seavey et a1 July 31, 1956 2,767,655 Seavey Oct. 23, 1956 2,777,389 Lawrence Jan. 15, 1957 

1. A METHOD OF SEALING AN ELECTRIC BLASTING CAP HAVING A METALLIC CASE OPEN AT ONE END AND CONTAINING AN EXPLOSIVE CHARGE COMPRISING, INSERTING A BRIDGE PLUG CARRYING A PAIR OF SPACED LEAD WIRES INTO THE CASE AND ABOVE THE EXPLOSIVE CHARAGE, CRIMPING THE OPEN END OF THE CASE ABOUT AND BETWEEN THE LEAD WIRES ABOVE THE BRIDGE PLUG, THE CRIMPING BEING RESTRICTED TO THAT PORTION OF THE CASE ABOVE THE BRIDGE PLUG, SUBSTANTIALLY FILLING THAT PORTION OF THE CASE ABOVE THE BRIDGE PLUG WITH A LIQUID POLYMERIZABLE ELASTOMER, AND POLYMERIZING THE ELASTOMER, THE ELASTOMER POLYMERIZED IN PLACE CONSTITUTING THE SOLE MEANS OF SEALING THE BLASTING CAP. 